Conventionally, as display devices, a liquid-crystal display (LCD) having liquid-crystal cells with a liquid-crystal layer retained between paired substrates and an organic electroluminescence display device which uses an organic electroluminescence material as a light-emitting element (organic electroluminescence element) of a display part have been known. For example, as described in Japanese Patent Application Laid-Open No. 2012-252359, a display device of any of the above includes an optical sensor such as a photodiode, and can thereby adjust the luminance of an image to be display in accordance with peripheral illuminance.